Gamma-ray Burst 251003A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

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Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 03 Oct 25 01:58:50 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     1400964,   Seg_Num: 0
GRB_RA:           18.503d {+01h 14m 01s} (J2000),
                  18.903d {+01h 15m 37s} (current),
                  17.733d {+01h 10m 56s} (1950)
GRB_DEC:         +56.507d {+56d 30' 23"} (J2000),
                 +56.642d {+56d 38' 32"} (current),
                 +56.242d {+56d 14' 31"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       3195 [cnts]    Image_Peak=183 [image_cnts]
TRIGGER_DUR:     1.024 [sec] 
TRIGGER_INDEX:   146     E_range: 25-100 keV
BKG_INTEN:       18704 [cnts]
BKG_TIME:        7091.56 SOD {01:58:11.56} UT
BKG_DUR:         8 [sec]
GRB_DATE:        20951 TJD;   276 DOY;   25/10/03
GRB_TIME:        7110.06 SOD {01:58:30.06} UT
GRB_PHI:          50.17 [deg]
GRB_THETA:         9.66 [deg]
SOLN_STATUS:     0x20000003
RATE_SIGNIF:     15.45 [sigma]
IMAGE_SIGNIF:    8.18 [sigma]
MERIT_PARAMS:     +1  +0  +0  +0  +2  -1  +0  +1 +60  +0 
SUN_POSTN:       189.30d {+12h 37m 12s}   -4.01d {-04d 00' 25"}
SUN_DIST:        126.81 [deg]   Sun_angle= 11.4 [hr] (West of Sun)
MOON_POSTN:      319.61d {+21h 18m 26s}  -18.57d {-18d 34' 05"}
MOON_DIST:        89.99 [deg]
MOON_ILLUM:      79 [%]
GAL_COORDS:      126.06, -6.23 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       43.26, 44.06 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Coordinates.  
COMMENTS:        This is a rate trigger.  
COMMENTS:        A point_source was found.  
COMMENTS:        This does not match any source in the on-board catalog.  
COMMENTS:        This does not match any source in the ground catalog.  
COMMENTS:        This is a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 356.67,18.82 [deg].  
COMMENTS:           
COMMENTS:        NOTE: This BAT event is temporally(1.0<100sec) coincident with the FERMI_GBM event (trignum=781149516).

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Fri 03 Oct 25 01:59:00 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      47
TRIGGER_NUM:     781149516
GRB_RA:            7.517d {+00h 30m 04s} (J2000),
                   7.877d {+00h 31m 31s} (current),
                   6.821d {+00h 27m 17s} (1950)
GRB_DEC:         +57.783d {+57d 46' 60"} (J2000),
                 +57.925d {+57d 55' 31"} (current),
                 +57.507d {+57d 30' 25"} (1950)
GRB_ERROR:       31.13 [deg radius, statistical plus systematic]
GRB_INTEN:       51 [cnts/sec]
DATA_SIGNIF:     5.00 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        20951 TJD;   276 DOY;   25/10/03
GRB_TIME:        7111.96 SOD {01:58:31.96} UT
GRB_PHI:         186.00 [deg]
GRB_THETA:        55.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO:      1.16
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      96%  GRB
2nd_MOST_LIKELY:   1%  Generic SGR
DETECTORS:       0,0,0, 0,0,0, 1,1,0, 0,0,1, 0,0,
SUN_POSTN:       189.30d {+12h 37m 12s}   -4.01d {-04d 00' 25"}
SUN_DIST:        126.07 [deg]   Sun_angle= -11.9 [hr] (East of Sun)
MOON_POSTN:      319.61d {+21h 18m 26s}  -18.57d {-18d 34' 03"}
MOON_DIST:        86.26 [deg]
MOON_ILLUM:      79 [%]
GAL_COORDS:      120.08, -4.97 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       37.15, 48.46 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251003082/quicklook/glg_lc_medres34_bn251003082.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 195.97,20.40 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(1.0<100sec) coincident with the SWIFT_BAT event (trignum=1400964).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Fri 03 Oct 25 01:59:18 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      57
TRIGGER_NUM:     781149516
GRB_RA:            8.380d {+00h 33m 31s} (J2000),
                   8.740d {+00h 34m 58s} (current),
                   7.685d {+00h 30m 44s} (1950)
GRB_DEC:         +54.830d {+54d 49' 48"} (J2000),
                 +54.972d {+54d 58' 18"} (current),
                 +54.554d {+54d 33' 16"} (1950)
GRB_ERROR:       14.17 [deg radius, statistical only]
DATA_SIGNIF:     5.40 [sigma]
DATA_INTERVAL:   4.096 [sec]
GRB_DATE:        20951 TJD;   276 DOY;   25/10/03
GRB_TIME:        7111.96 SOD {01:58:31.96} UT
GRB_PHI:         186.00 [deg]
GRB_THETA:        58.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:       189.30d {+12h 37m 12s}   -4.01d {-04d 00' 26"}
SUN_DIST:        129.03 [deg]   Sun_angle= -12.0 [hr] (East of Sun)
MOON_POSTN:      319.61d {+21h 18m 27s}  -18.57d {-18d 34' 00"}
MOON_DIST:        84.53 [deg]
MOON_ILLUM:      80 [%]
GAL_COORDS:      120.33, -7.95 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       35.21, 45.77 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251003082/quicklook/glg_lc_medres34_bn251003082.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_781149516.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        In the LAT Field-of-view.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(1.0<100sec) coincident with the SWIFT_BAT event (trignum=1400964).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Fri 03 Oct 25 02:07:56 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     781149516
GRB_RA:           31.890d {+02h 07m 34s} (J2000),
                  32.310d {+02h 09m 14s} (current),
                  31.079d {+02h 04m 19s} (1950)
GRB_DEC:         +49.630d {+49d 37' 48"} (J2000),
                 +49.751d {+49d 45' 05"} (current),
                 +49.393d {+49d 23' 33"} (1950)
GRB_ERROR:       18.23 [deg radius, statistical only]
GRB_DATE:        20951 TJD;   276 DOY;   25/10/03
GRB_TIME:        7111.96 SOD {01:58:31.96} UT
GRB_PHI:         202.00 [deg]
GRB_THETA:        64.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       189.31d {+12h 37m 14s}   -4.01d {-04d 00' 34"}
SUN_DIST:        130.29 [deg]   Sun_angle= 10.5 [hr] (West of Sun)
MOON_POSTN:      319.69d {+21h 18m 45s}  -18.54d {-18d 32' 11"}
MOON_DIST:        93.42 [deg]
MOON_ILLUM:      80 [%]
GAL_COORDS:      135.37,-11.39 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       48.29, 34.26 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251003082/quicklook/glg_lc_medres34_bn251003082.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251003082/quicklook/glg_locplot_all_bn251003082.png
COMMENTS:        Fermi-GBM Final Position.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file should be available by the time this FINAL notice is produced.  
COMMENTS:        This notice was generated completely by automated pipeline processing.  
COMMENTS:        In the LAT Field-of-view.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(1.0<100sec) coincident with the SWIFT_BAT event (trignum=1400964).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 03 Oct 25 02:00:20 UT
NOTICE_TYPE:     Swift-XRT Image
TRIGGER_NUM:     1400964,   Seg_Num: 0
GRB_RA:           18.5279d {+01h 14m 06.6s} (J2000),
                  18.9276d {+01h 15m 42.6s} (current),
                  17.7571d {+01h 11m 01.7s} (1950)
GRB_DEC:         +56.4908d {+56d 29' 26.8"} (J2000),
                 +56.6266d {+56d 37' 35.7"} (current),
                 +56.2262d {+56d 13' 34.4"} (1950)
GRB_ERROR:       5.0 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       58 [cnts]
IMG_START_DATE:  20951 TJD;   276 DOY;   25/10/03
IMG_START_TIME:  7182.15 SOD {01:59:42.15} UT,   72.1 [sec] since BAT Trigger Time
CENTROID_X:      331.31,  raw= 331  [pixels]
CENTROID_Y:      277.25,  raw= 277  [pixels]
ROLL:            11.52 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   -50.55
GRB_POS_XRT_Z:   46.48
IMAGE_URL:       sw01400964000msxps_rw.img
SUN_POSTN:       189.30d {+12h 37m 13s}   -4.01d {-04d 00' 27"}
SUN_DIST:        126.83 [deg]   Sun_angle= 11.4 [hr] (West of Sun)
MOON_POSTN:      319.62d {+21h 18m 29s}  -18.56d {-18d 33' 46"}
MOON_DIST:        89.98 [deg]
MOON_ILLUM:      80 [%]
GAL_COORDS:      126.08, -6.24 [deg] galactic lon,lat of the burst
ECL_COORDS:       43.26, 44.04 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 03 Oct 25 02:00:22 UT
NOTICE_TYPE:     Swift-XRT Processed Image
TRIGGER_NUM:     1400964,   Seg_Num: 0
GRB_RA:           18.5279d {+01h 14m 06.6s} (J2000),
                  18.9276d {+01h 15m 42.6s} (current),
                  17.7571d {+01h 11m 01.7s} (1950)
GRB_DEC:         +56.4908d {+56d 29' 26.8"} (J2000),
                 +56.6266d {+56d 37' 35.7"} (current),
                 +56.2262d {+56d 13' 34.4"} (1950)
GRB_ERROR:       5.0 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       58 [cnts]
IMG_START_DATE:  20951 TJD;   276 DOY;   25/10/03
IMG_START_TIME:  7182.15 SOD {01:59:42.15} UT,   72.1 [sec] since BAT Trigger Time
CENTROID_X:      331.31,  raw= 331  [pixels]
CENTROID_Y:      277.25,  raw= 277  [pixels]
ROLL:            11.52 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   -50.55
GRB_POS_XRT_Z:   46.48
IMAGE_URL:       sw01400964000msxps_rw.img
SUN_POSTN:       189.30d {+12h 37m 13s}   -4.01d {-04d 00' 27"}
SUN_DIST:        126.83 [deg]   Sun_angle= 11.4 [hr] (West of Sun)
MOON_POSTN:      319.62d {+21h 18m 29s}  -18.56d {-18d 33' 46"}
MOON_DIST:        89.98 [deg]
MOON_ILLUM:      80 [%]
GAL_COORDS:      126.08, -6.24 [deg] galactic lon,lat of the burst
ECL_COORDS:       43.26, 44.04 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Processed Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 03 Oct 25 02:00:10 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     1400964,   Seg_Num: 0
GRB_RA:           18.5279d {+01h 14m 06.69s} (J2000),
                  18.9276d {+01h 15m 42.62s} (current),
                  17.7571d {+01h 11m 01.70s} (1950)
GRB_DEC:         +56.4908d {+56d 29' 26.8"} (J2000),
                 +56.6266d {+56d 37' 35.7"} (current),
                 +56.2262d {+56d 13' 34.4"} (1950)
GRB_ERROR:       5.2 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.66e-09 [erg/cm2/sec]
GRB_SIGNIF:      7.61 [sigma]
IMG_START_DATE:  20951 TJD;   276 DOY;   25/10/03
IMG_START_TIME:  7182.15 SOD {01:59:42.15} UT,   72.1 [sec] since BAT Trigger Time
TAM[0-3]:        327.63 237.13 261.61 243.84
AMPLIFIER:       2
WAVEFORM:        134
SUN_POSTN:       189.30d {+12h 37m 13s}   -4.01d {-04d 00' 26"}
SUN_DIST:        126.83 [deg]   Sun_angle= 11.4 [hr] (West of Sun)
MOON_POSTN:      319.62d {+21h 18m 29s}  -18.56d {-18d 33' 48"}
MOON_DIST:        89.98 [deg]
MOON_ILLUM:      80 [%]
GAL_COORDS:      126.08, -6.24 [deg] galactic lon,lat of the burst
ECL_COORDS:       43.26, 44.04 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        The XRT position is 1.24 arcmin from the BAT position.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 03 Oct 25 02:02:44 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1400964,   Seg_Num: 0
POINT_RA:         18.508d {+01h 14m 02s} (J2000)
POINT_DEC:       +56.506d {+56d 30' 22"} (J2000)
POINT_ROLL:      11.525d
IMG_START_DATE:  20951 TJD;   276 DOY;   25/10/03
IMG_START_TIME:  7188.99 SOD {01:59:48.99} UT,   78.9 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.104
N_STARS:         190
X_OFFSET:        456 [pixels]
Y_OFFSET:        560 [pixels]
X_MAX:           1415 [pixels]
Y_MAX:           1519 [pixels]
DET_THRESH:      12
PHOTO_THRESH:    6
SL_URL:          sw01400964000msufc0078.fits
SUN_POSTN:       189.30d {+12h 37m 13s}   -4.01d {-04d 00' 29"}
SUN_DIST:        126.81 [deg]   Sun_angle= 11.4 [hr] (West of Sun)
MOON_POSTN:      319.64d {+21h 18m 34s}  -18.55d {-18d 33' 16"}
MOON_DIST:        89.96 [deg]
MOON_ILLUM:      80 [%]
GAL_COORDS:      126.06, -6.23 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       43.26, 44.06 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 03 Oct 25 02:02:57 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1400964,   Seg_Num: 0
POINT_RA:         18.508d {+01h 14m 02s} (J2000)
POINT_DEC:       +56.506d {+56d 30' 22"} (J2000)
POINT_ROLL:      11.525d
IMG_START_DATE:  20951 TJD;   276 DOY;   25/10/03
IMG_START_TIME:  7188.99 SOD {01:59:48.99} UT,   78.9 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.104
N_STARS:         190
X_OFFSET:        456 [pixels]
Y_OFFSET:        560 [pixels]
X_MAX:           1415 [pixels]
Y_MAX:           1519 [pixels]
DET_THRESH:      12
PHOTO_THRESH:    6
SL_URL:          sw01400964000msufc0078.fits
SUN_POSTN:       189.30d {+12h 37m 13s}   -4.01d {-04d 00' 29"}
SUN_DIST:        126.81 [deg]   Sun_angle= 11.4 [hr] (West of Sun)
MOON_POSTN:      319.64d {+21h 18m 35s}  -18.55d {-18d 33' 13"}
MOON_DIST:        89.96 [deg]
MOON_ILLUM:      80 [%]
GAL_COORDS:      126.06, -6.23 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       43.26, 44.06 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Source List.  
COMMENTS:        All 4 attachments are included.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 03 Oct 25 02:04:14 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1400964,   Seg_Num: 0
POINT_RA:         18.508d {+01h 14m 02s} (J2000)
POINT_DEC:       +56.506d {+56d 30' 22"} (J2000)
ROLL:            11.525d
IMG_START_DATE:  20951 TJD;   276 DOY;   25/10/03
IMG_START_TIME:  7188.99 SOD {01:59:48.99} UT,   78.9 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     781149625
X_OFFSET:        759 [pixels]
Y_OFFSET:        1022 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       919
Y_GRB_POS:       1182
BINNING_INDEX:   1
IM_URL:          sw01400964000msuni0115.fits
SUN_POSTN:       189.31d {+12h 37m 13s}   -4.01d {-04d 00' 30"}
SUN_DIST:        126.81 [deg]   Sun_angle= 11.4 [hr] (West of Sun)
MOON_POSTN:      319.66d {+21h 18m 37s}  -18.55d {-18d 32' 57"}
MOON_DIST:        89.95 [deg]
MOON_ILLUM:      80 [%]
GAL_COORDS:      126.06, -6.23 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       43.26, 44.06 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Image.  
COMMENTS:        The GRB Position came from the XRT Position Command.  
COMMENTS:        The image has 2x2 binning (compression).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 03 Oct 25 02:04:29 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1400964,   Seg_Num: 0
POINT_RA:         18.508d {+01h 14m 02s} (J2000)
POINT_DEC:       +56.506d {+56d 30' 22"} (J2000)
ROLL:            11.525d
IMG_START_DATE:  20951 TJD;   276 DOY;   25/10/03
IMG_START_TIME:  7188.99 SOD {01:59:48.99} UT,   78.9 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     781149625
X_OFFSET:        759 [pixels]
Y_OFFSET:        1022 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       919
Y_GRB_POS:       1182
BINNING_INDEX:   1
IM_URL:          sw01400964000msuni0115.fits
SUN_POSTN:       189.31d {+12h 37m 13s}   -4.01d {-04d 00' 31"}
SUN_DIST:        126.81 [deg]   Sun_angle= 11.4 [hr] (West of Sun)
MOON_POSTN:      319.66d {+21h 18m 38s}  -18.55d {-18d 32' 54"}
MOON_DIST:        89.95 [deg]
MOON_ILLUM:      80 [%]
GAL_COORDS:      126.06, -6.23 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       43.26, 44.06 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Image.  
COMMENTS:        The GRB Position came from the XRT Position Command.  
COMMENTS:        The image has 2x2 binning (compression).  
COMMENTS:        All 4 attachments are included.

GCN Circular #42068
V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
MASTER-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the Swift GRB251003.08 (trigger No 1400964,01h 14m 00.72s , +56d 30m 25.2s, R=0.05) errorbox 10 sec after notice time and 34 sec after trigger time at 2025-10-03 01:59:04 UT, with upper limit up to 16.6 mag. Observations started at twilight. The observations began at zenith distance = 43 deg. The sun altitude is -13.7 deg.
The galactic latitude b = -6 deg., longitude l = 126 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3005736
We obtain a following upper limits.
```
Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

      40 |   MASTER-Kislovodsk |  P- |    10 | 15.8 |        
      50 |   MASTER-Kislovodsk |  P- |    30 | 16.4 |  Coadd 
      40 |   MASTER-Kislovodsk |  P| |    10 | 14.6 |        
      58 |   MASTER-Kislovodsk |  P- |    10 | 16.0 |        
      58 |   MASTER-Kislovodsk |  P| |    10 | 15.0 |        
      77 |   MASTER-Kislovodsk |  P- |    10 | 16.2 |        
      77 |   MASTER-Kislovodsk |  P| |    10 | 15.1 |        
     100 |   MASTER-Kislovodsk |  P- |    20 | 16.5 |        
     100 |   MASTER-Kislovodsk |  P| |    20 | 15.8 |        
     129 |   MASTER-Kislovodsk |  P- |    20 | 16.5 |        
     129 |   MASTER-Kislovodsk |  P| |    20 | 15.6 |        
     162 |   MASTER-Kislovodsk |  P- |    30 | 16.6 |        
     162 |   MASTER-Kislovodsk |  P| |    30 | 15.9 |        
```
The observation and reduction will continue. The message may be cited.
GCN Circular #42069
The Fermi GBM team reports the detection of a likely LONG GRB
At 01:58:31 UT on 3 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251003A (trigger 781149516.956282 / 251003082).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 31.9, Dec = 49.6 (J2000 degrees, equivalent to J2000 02h 07m, 49d 36'), with a statistical uncertainty of 18.2 degrees.
The angle from the Fermi LAT boresight is 64.0 degrees.
The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251003082/quicklook/glg_skymap_all_bn251003082.png
The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251003082/quicklook/glg_healpix_all_bn251003082.fit
The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251003082/quicklook/glg_lc_medres34_bn251003082.gif
GCN Circular #42070
A. P. Beardmore (U Leicester), R. Gupta (NASA GSFC), K. L. Page (U Leicester) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team:
At 01:58:30 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 251003A (trigger=1400964). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 18.503, +56.507 which is
```
   RA(J2000) = 01h 14m 01s
   Dec(J2000) = +56d 30' 23"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 20 sec. The peak count rate was ~1835 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 01:59:42.1 UT, 72.1 seconds after the BAT trigger. Using promptly downlinked data we find a bright, fading, uncatalogued X-ray source located at RA, Dec 18.52734, 56.49009 which is equivalent to:
```
   RA(J2000)  = 01h 14m 06.56s
   Dec(J2000) = +56d 29' 24.3"
```
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This location is 77 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper.
A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 4.39 x 10^21 cm^-2 (Willingale et al. 2013).
The initial flux in the 2.5 s image was 1.66e-09 erg cm^-2 s^-1 (0.2-10 keV).
UVOT took a finding chart exposure of 150 seconds with the White filter starting 78 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.408.
Burst Advocate for this burst is A. P. Beardmore (apb AT star.le.ac.uk). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/)
GCN Circular #42071
P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:
Using 263 s of promptly downlinked XRT event data for GRB 251003A, we find an enhanced XRT position of the afterglow: RA, Dec: 18.52838, 56.49082 which is equivalent to:
```
   RA (J2000)  = 01 14 06.81
   Dec (J2000) = +56 29 26.9
```
with an uncertainty of 2.3 arcseconds (radius, 90% confidence). Analysis of the promptly available data is online at http://www.swift.ac.uk/sper/1400964.
Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177).
This circular is an official product of the Swift-XRT team.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 03 Oct 25 02:04:22 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     1400964,   Seg_Num: 0
GRB_RA:           18.503d {+01h 14m 01s} (J2000),
                  18.903d {+01h 15m 37s} (current),
                  17.733d {+01h 10m 56s} (1950)
GRB_DEC:         +56.507d {+56d 30' 23"} (J2000),
                 +56.642d {+56d 38' 32"} (current),
                 +56.242d {+56d 14' 31"} (1950)
GRB_DATE:        20951 TJD;   276 DOY;   25/10/03
GRB_TIME:        7110.06 SOD {01:58:30.06} UT
TRIGGER_INDEX:   146
GRB_PHI:          50.17 [deg]
GRB_THETA:         9.66 [deg]
DELTA_TIME:      71.00 [sec]
TRIGGER_DUR:     1.024 [sec] 
SOLN_STATUS:     0x2003
RATE_SIGNIF:     15.45 [sigma]
IMAGE_SIGNIF:    8.18 [sigma]
LC_URL:          sw01400964000msb.lc
SUN_POSTN:       189.31d {+12h 37m 13s}   -4.01d {-04d 00' 30"}
SUN_DIST:        126.81 [deg]   Sun_angle= 11.4 [hr] (West of Sun)
MOON_POSTN:      319.66d {+21h 18m 38s}  -18.55d {-18d 32' 55"}
MOON_DIST:        89.95 [deg]
MOON_ILLUM:      80 [%]
GAL_COORDS:      126.06, -6.23 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       43.26, 44.06 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Lightcurve.  
COMMENTS:           
COMMENTS:        The next comments were copied from the BAT_POS Notice:  
COMMENTS:        This is a rate trigger.  
COMMENTS:        A point_source was found.  
COMMENTS:        This does not match any source in the on-board catalog.  
COMMENTS:        This does not match any source in the ground catalog.  
COMMENTS:        There is a bright star (mag=3.89) 11.36 arcmin from this position.  
COMMENTS:        This is a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 356.67,18.82 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 03 Oct 25 02:10:53 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1400964,   Seg_Num: 0
POINT_RA:         18.506d {+01h 14m 01s} (J2000)
POINT_DEC:       +56.508d {+56d 30' 28"} (J2000)
POINT_ROLL:      11.523d
IMG_START_DATE:  20951 TJD;   276 DOY;   25/10/03
IMG_START_TIME:  7400.97 SOD {02:03:20.97} UT,   290.9 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.529
N_STARS:         128
X_OFFSET:        439 [pixels]
Y_OFFSET:        702 [pixels]
X_MAX:           1398 [pixels]
Y_MAX:           1661 [pixels]
DET_THRESH:      7
PHOTO_THRESH:    3
SL_URL:          sw01400964000msufc0290.fits
SUN_POSTN:       189.31d {+12h 37m 14s}   -4.01d {-04d 00' 37"}
SUN_DIST:        126.82 [deg]   Sun_angle= 11.4 [hr] (West of Sun)
MOON_POSTN:      319.72d {+21h 18m 52s}  -18.53d {-18d 31' 33"}
MOON_DIST:        89.91 [deg]
MOON_ILLUM:      80 [%]
GAL_COORDS:      126.06, -6.23 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       43.26, 44.06 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 03 Oct 25 02:12:27 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1400964,   Seg_Num: 0
POINT_RA:         18.506d {+01h 14m 01s} (J2000)
POINT_DEC:       +56.508d {+56d 30' 28"} (J2000)
ROLL:            11.523d
IMG_START_DATE:  20951 TJD;   276 DOY;   25/10/03
IMG_START_TIME:  7400.97 SOD {02:03:20.97} UT,   290.9 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     781149837
X_OFFSET:        759 [pixels]
Y_OFFSET:        1022 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       919
Y_GRB_POS:       1182
BINNING_INDEX:   1
IM_URL:          sw01400964000msuni0327.fits
SUN_POSTN:       189.31d {+12h 37m 14s}   -4.01d {-04d 00' 38"}
SUN_DIST:        126.82 [deg]   Sun_angle= 11.4 [hr] (West of Sun)
MOON_POSTN:      319.73d {+21h 18m 55s}  -18.52d {-18d 31' 14"}
MOON_DIST:        89.90 [deg]
MOON_ILLUM:      80 [%]
GAL_COORDS:      126.06, -6.23 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       43.26, 44.06 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Image.  
COMMENTS:        The GRB Position came from the XRT Position Command.  
COMMENTS:        The image has 2x2 binning (compression).  
COMMENTS:        All 4 attachments are included.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 03 Oct 25 02:11:08 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1400964,   Seg_Num: 0
POINT_RA:         18.506d {+01h 14m 01s} (J2000)
POINT_DEC:       +56.508d {+56d 30' 28"} (J2000)
POINT_ROLL:      11.523d
IMG_START_DATE:  20951 TJD;   276 DOY;   25/10/03
IMG_START_TIME:  7400.97 SOD {02:03:20.97} UT,   290.9 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.529
N_STARS:         128
X_OFFSET:        439 [pixels]
Y_OFFSET:        702 [pixels]
X_MAX:           1398 [pixels]
Y_MAX:           1661 [pixels]
DET_THRESH:      7
PHOTO_THRESH:    3
SL_URL:          sw01400964000msufc0290.fits
SUN_POSTN:       189.31d {+12h 37m 14s}   -4.01d {-04d 00' 37"}
SUN_DIST:        126.82 [deg]   Sun_angle= 11.4 [hr] (West of Sun)
MOON_POSTN:      319.72d {+21h 18m 52s}  -18.53d {-18d 31' 30"}
MOON_DIST:        89.90 [deg]
MOON_ILLUM:      80 [%]
GAL_COORDS:      126.06, -6.23 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       43.26, 44.06 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Source List.  
COMMENTS:        All 4 attachments are included.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 03 Oct 25 02:11:29 UT
NOTICE_TYPE:     Swift-XRT Position UPDATE
TRIGGER_NUM:     1400964,   Seg_Num: 0
GRB_RA:           18.5286d {+01h 14m 06.86s} (J2000),
                  18.9283d {+01h 15m 42.79s} (current),
                  17.7578d {+01h 11m 01.87s} (1950)
GRB_DEC:         +56.4907d {+56d 29' 26.5"} (J2000),
                 +56.6265d {+56d 37' 35.3"} (current),
                 +56.2261d {+56d 13' 34.0"} (1950)
GRB_ERROR:       2.4 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.00e-10 [erg/cm2/sec]
GRB_SIGNIF:      10.00 [sigma]
IMG_START_DATE:  20951 TJD;   276 DOY;   25/10/03
IMG_START_TIME:  7316.00 SOD {02:01:56.00} UT,   205.9 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:       189.31d {+12h 37m 14s}   -4.01d {-04d 00' 37"}
SUN_DIST:        126.83 [deg]   Sun_angle= 11.4 [hr] (West of Sun)
MOON_POSTN:      319.72d {+21h 18m 53s}  -18.52d {-18d 31' 26"}
MOON_DIST:        89.90 [deg]
MOON_ILLUM:      80 [%]
GAL_COORDS:      126.08, -6.24 [deg] galactic lon,lat of the burst
ECL_COORDS:       43.26, 44.04 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        This is an Update Notice -- the RA,Dec values herein supersede the previous XRT_POS Notice.  
COMMENTS:        TAM values, flux and significance fields are not valid.  
COMMENTS:        This position was automatically generated on the ground using  
COMMENTS:        Photon Counting data telemetered via TDRSS (SPER data).  
COMMENTS:        See http://www.swift.ac.uk/sper/docs.php for details.  
COMMENTS:        This position was enhanced using UVOT field astrometry.  
COMMENTS:        The probability that this is a serendipitous source in the  
COMMENTS:        SPER window is 0.11% < P(seren) < 0.58%.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 03 Oct 25 02:12:14 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1400964,   Seg_Num: 0
POINT_RA:         18.506d {+01h 14m 01s} (J2000)
POINT_DEC:       +56.508d {+56d 30' 28"} (J2000)
ROLL:            11.523d
IMG_START_DATE:  20951 TJD;   276 DOY;   25/10/03
IMG_START_TIME:  7400.97 SOD {02:03:20.97} UT,   290.9 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     781149837
X_OFFSET:        759 [pixels]
Y_OFFSET:        1022 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       919
Y_GRB_POS:       1182
BINNING_INDEX:   1
IM_URL:          sw01400964000msuni0327.fits
SUN_POSTN:       189.31d {+12h 37m 14s}   -4.01d {-04d 00' 38"}
SUN_DIST:        126.82 [deg]   Sun_angle= 11.4 [hr] (West of Sun)
MOON_POSTN:      319.73d {+21h 18m 55s}  -18.52d {-18d 31' 16"}
MOON_DIST:        89.90 [deg]
MOON_ILLUM:      80 [%]
GAL_COORDS:      126.06, -6.23 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       43.26, 44.06 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Image.  
COMMENTS:        The GRB Position came from the XRT Position Command.  
COMMENTS:        The image has 2x2 binning (compression).

GCN Circular #42072
F. J. Aceituno, R. Sanchez-Ramirez A. J. Castro-Tirado, S. Guziy, M.D. Caballero-Garcia, S.-Y. Wu and I. Perez-Garcia (IAA-CSIC), and Y.-D. Hu (GXI), on behalf of a larger collaboration, report:
Following the detection of GRB 251003A by both Fermi (Fermi team, GCNC 42069) and Swift (Beardmore et al. GCNC 42070), we obtained a 300s exposure image (I-band) with the 1.5m OSN telescope in Sierra Nevada (Granada, Spain) starting on Oct 3 (02:34 UT, i.e. 36 min post burst). At the enhanced X-ray position (Evans et al. GCNC 42071) we identify an optical source with a preliminary magnitude of 21, which we propose to be the afterglow to GRB 251003A. Further observations are being gathered.
GCN Circular #42073
Enrique Moreno Méndez (UNAM), Benjamin Schneider (LAM), Camila Angulo (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), and Antonio de Ugarte Postigo (LAM):
We imaged the field of the Swift GRB 251003A (Beardmore et al., GCN Circ. 42070) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-03 02:19 to 02:22 UTC (from 0.3 to 0.7 hours after the trigger) and obtained 3 minutes of simultaneous exposure in the r and z filters.
The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.
We detected the optical counterpart reported by Aceituno et al., GCN Circ. 42072, at a position of RA, Dec = 18.52939, 56.49110 (J2000), with preliminary magnitudes of:
```
r = 20.34 +/- 0.11
z = 18.56 +/- 0.05
```
The object fades in subsequent observations, confirming that it is the optical afterglow.
The very red color suggests that this might be either a moderate redshift GRB with a drop-out in r or a very heavily reddened GRB.
Further observations in g/r/i/z/y are ongoing.
We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams.
COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.
GCN Circular #42074
R. Strausbaugh (Eastern Illinois University), A. Cucchiara (NASA) report on behalf of a larger collaboration:
We observed the Swift GRB 251003A field (Beardmore et al., GCN 42070) with the LCOGT 1-meter Sinistro instrument at the McDonald Observatory, USA site, on October 3, from 03:07 to 03:39 UT (corresponding to 1.15 to 1.68 hours after the GRB trigger time) with the SDSS i and r filters.
We performed a series of 3x300s exposures in i-band and r-band. We detect an uncatalogued source in the XRT enhanced error region (Evans et al. GCNC 42071) consistent with other optical counterpart observations (Aceituno et al., GCN 42072; Méndez et al., GCN 42073) in both bands. We note that the r-i color of this event may indicate a moderate redshift source (z>4).
The following magnitudes are calculated using the PanSTARRS catalog as reference:
```
r = 20.97 +/- 0.12
i = 19.25 +/- 0.04
```
These magnitudes are not corrected for galactic extinction.
GCN Circular #42085
M. Freeberg (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), S. Antier (OCA/IJCLab), M. Coughlin (UMN),S. Karpov (FZU), P. Hello (IJCLAB), M. Pillas (IAP) on behalf of the GRANDMA/Kilonova-Catcher collaboration:
We observed the field of GRB 251003A detected by Fermi/GBM (Fermi GBM team, GCN 42069) and Swift/BAT (Beardmore et al., GCN 42070) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the TEC160FL operated by M. Freeberg. Our observations started at TGRB+1.2hr.
In our stacked frames, subtracted from the PanSTARRS DR2 template image, we detect the optical counterpart reported by OSN (Aceituno et al., GCN 42072), COLIBRI (Moreno Méndez et al., GCN 42073), LCO-1m (Strausbaugh et al., GCN 42074).
We report our follow-up results in the table below
```
+---------------+-----------+--------+----------------+------------+
| Tmid-TGRB (hr)| Exp (s)   | Filter | Magnitude      | Instrument |
+===============+===========+========+================+============+
| 1.71          | 20 x 180s | r (AB) | 21.07 +/- 0.37 | TEC160FL   | 
| 3.58          | 25 x 180s | i (AB) | 19.14 +/- 0.18 | TEC160FL   | 
+---------------+-----------+--------+----------------+------------+
```
As also pointed out by (Moreno Méndez et al., GCN 42073, Strausbaugh et al., GCN 42074), the r-i color index we measure indicates a very red afterglow and further observations at infrared wavelengths and spectroscopic observations are encouraged to disentangle whether this burst is highly extinguished or localized at a moderately high redshift.
All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the sloan filters were calibrated using the PanSTARRS DR1 catalog.
We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023).
GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/).
GCN Circular #42086
R. Sanchez-Ramirez, A. J. Castro-Tirado, S. Guziy, M.D. Caballero-Garcia, S.-Y. Wu and I. Perez-Garcia (IAA-CSIC), Y.-D. Hu (GXI), R. Scarpa (GTC, IAC), D. Gonzalez (GTC), A. Cabrera-Lavers (GTC, IAC), S. B. Pandey (ARIES), M. Gritsevich (Univ. of Helsinki), J. Becerra-Gonzalez (IAC), L. Piro (INAF/IAPS) and B.-B. Zhang (NJU), on behalf of a larger collaboration, report:
Following the detection of GRB 251003A by Fermi (Fermi Team, GCN 42069) and Swift (Beardmore et al. GCN 42070, Evans et al. GCN 42071), we observed the optical afterglow (Aceituno et al., GCN 42072, Moreno Mendez et al., GCN 42073, Strausbaugh et al., GCN 42074) with the 10.4m GTC telescope, at the Spanish Roque de los Muchachos Observatory, on the island of La Palma, equipped with the OSIRIS+ instrument.
The spectroscopic observations consisted of 2x900s exposures using grism R1000B, and 1x900s using R2500I, covering the spectral range between 3,600 and 10,000 A. The observations started on Oct 3, 03:12 UT (i.e. 1.22 h after the burst trigger).
From a preliminary reduction, we find a strong DLA at ~6500A with its corresponding Lyman break at ~5000A. Several metal absorption lines are detected as well, which we interpret as coming from SiII, SiII*, CII, SiIV, CIV, FeII, FeII*, NiII, AlII, AlIII, all at z=4.412. The detection of fine structure lines links this system to the GRB.
GCN Circular #42088
P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) report on behalf of the Swift-XRT team.
Using 1392 s of XRT Photon Counting mode data and 4 UVOT images for GRB 251003A, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 18.52924, +56.49080 which is equivalent to:
```
RA (J2000): 01h 14m 07.02s
Dec (J2000): +56d 29' 26.9"
```
with an uncertainty of 2.5 arcsec (radius, 90% confidence).
This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177).
This circular was automatically generated, and is an official product of the Swift-XRT team.
GCN Circular #42094
I. Worssam, B. P. Gompertz, D. O’Neill, M. E. Wortley, G. Ramsay, R. Starling, M. Kennedy, B. Godson, J. Lyman, K. Ackley, M. J. Dyer, K. Ulaczyk, A. Kumar,, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration:
We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to GRB 251003A (Fermi GBM team, GCN 42069; Beardmore et al. GCN 42070). Targeted observations were performed at 2025-10-03 02:03:05 (4.57mins post trigger) and 2025-10-03 03:11:32 (1.22h post trigger). Each observation consisted of 4x90s exposures in the GOTO L-band (400-700 nm). We detect the optical counterpart (Aceituno et al., GCN 42072; Méndez et al., GCN 42073; Strausbaugh et al., GCN 42074; Freeberg et al., GCN 42085; Sanchez-Ramirez et al., GCN 42086) with measured AB magnitudes of L = 19.94 ± 0.24 and L = 20.83 ± 0.28 for the two epochs respectively.
Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction.
GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC).
GCN Circular #42095
Benjamin Schneider (LAM), Ny Avo Rakotondrainibe (LAM), Enrique Moreno Méndez (UNAM), Antonio de Ugarte Postigo (LAM), Camila Angulo (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM) and Fredd Sánchez Álvarez (UNAM):
COLIBRÍ performed additional observations of the Fermi and Swift GRB 251003A (Fermi GBM team, GCN Circ. 42069; Beardmore et al., GCN Circ. 42070) starting from 2025-10-03 04:04:59 (2.1 hr after the trigger) and obtained images in the g, i, y filters. The photometry of the afterglow (Aceituno et al. GCN Circ. 42072; Moreno Méndez et al. GCN Circ. 42073; Strausbaugh et al. GCN Circ. 42074; Freeberg et al. GCN Circ. 42085; Worssam et al., GCN Circ. 42094) was performed using STDWeb/STDPipe (Karpov 2025), was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.
After combining data obtained from Moreno Méndez et al., GCN Circ. 42073 and correcting for the Galactic foreground extinction corresponding to a reddening of E(B-V) = 0.36 mag (Schlafly & Finkbeiner 2011), we fit a power-law model to the grizy-bands using the SMC extinction curve and we derive a photometric redshift of z = 4.38+0.07-0.04 (1-sigma c.l., statistical errors only). Our result is consistent with the GTC/OSIRIS+ redshift of z = 4.41 (Sanchez-Ramirez et al., GCN Circular 42086).
We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams.
COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.
GCN Circular #42096
D.N. Burrows (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-OAR), S. Lanava (PSU), S. Dichiara (PSU) and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 6.8 ks of XRT data for GRB 251003A, from 59 s to 34.6 ks after the trigger. The data comprise 126 s in Windowed Timing (WT) mode (the first 8 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode.
The late-time light curve (from T0+4.6 ks) can be modelled with a power-law decay with a decay index of alpha=0.6 (+0.4, -0.3).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.67 (+0.11, -0.10). The best-fitting absorption column is 1.4 (+3.0, -1.4) x 10^22 cm^-2, at a redshift of 4.412, in addition to the Galactic value of 4.4 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 2.8 x 10^-11 (7.5 x 10^-11) erg cm^-2 count^-1.
A summary of the WT-mode spectrum is thus:
```
Galactic foreground: 4.4 x 10^21 cm^-2
Intrinsic column:    1.4 (+3.0, -1.4) x 10^22 cm^-2 at z=4.412
Photon index:	     2.67 (+0.11, -0.10)
```
If the light curve continues to decay with a power-law decay index of 0.6, the count rate at T+24 hours will be 8.2 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.3 x 10^-13 (6.1 x 10^-13) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01400964.
This circular is an official product of the Swift-XRT team.
GCN Circular #42100
S. P. R. Shilling (Lancaster U.), M. De Pasquale (Univ. Messina) and A. P. Beardmore (U. Leicester) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 251003A 79 s after the BAT trigger (Beardmore et al., GCN Circ. 42070).
No optical afterglow consistent with the enhanced XRT position (Evans et al., GCN Circ. 42088) or those reported by other instruments (Aceituno et al., GCN Circ. 42072; Moreno Méndez et al., GCN Circ. 42073; Strausbaugh et al., GCN Circ. 42074; Worssam et al., GCN Circ. 42094), is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are:
```
 Filter         T_start(s)    T_stop(s)        Exp(s)         Mag

white                  79          229          147          >20.70
u                     291          474          180          >19.78
v                   33828        34558          711          >20.01
b                   43530        43837          298          >20.30
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.408 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #42126
R. Konno (WIS), S. Garrappa (WIS), E. A. Zimmerman (WIS), A. Horowicz (WIS), E. O. Ofek (WIS), S. Ben-Ami (WIS), D. Polishook (WIS), O. Yaron (WIS), S. Fainer (WIS), A. Krassilchtchikov (WIS), Y. M. Shani (WIS), E. Segre (WIS), A. Gal-Yam (WIS), and S. Spitzer (WIS) on behalf of the LAST Collaboration
We report observations of GRB 251003A, detected by Fermi (Fermi team, GCNC 42069) and Swift (Beardmore et al., GCNC 42070), with the Large Array Survey Telescope (LAST; Ofek et al. 2023 PASP 135, 5001; Ben-Ami et al. 2023 PASP 135, 5002).
We observe the field of GRB 251003A using 4 divergent telescopes, each with a FoV of 7.4 deg^2 and no filter (clear - similar to the GAIA Bp band) over several epochs. In each epoch, we coadd 20 images with each of 20s exposure. We detect a faint source coincident with the optical counterpart reported by Aceituno et al., GCN 42072; Méndez et al., GCN 42073; Strausbaugh et al., GCN 42074; Freeberg et al., GCN 42085; Sanchez-Ramirez et al., GCN 42086; Worssam et al., GCN 42094; Schneider et al., GCN 42095; Mo et al., GCN 42106.
The earliest detection with a 20x20s exposure image is confirmed at 2025-10-03 02:03:10 UTC (T-T0=280s) at an AB magnitude of 19.60 +/- 0.08.
LAST is a survey telescope array of the Weizmann Astrophysical Observatory (https://www.weizmann.ac.il/wao/).
GCN Circular #42170
Jacob Smith (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 01:58:31.96 UT on 03 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251003A (trigger 781149516/251003082), which was also detected by Swift BAT (A. P. Beardmore et al. 2025, GCN 42070). The Fermi GBM on-ground location is consistent with the Swift BAT position. GTC/OSIRIS+ detected a spectroscopic redshift z = 4.412 (R. Sanchez-Ramirez et al. 2025, GCN 42086).
The angle from the Fermi LAT boresight is 56 degrees.
The GBM light curve consists of a single emission episode with a duration (T90) of about 10 s (50-300 keV). The time-averaged spectrum from T0-4.1 to T0+6.1 s is best fit by a simple power law function with index -1.7 +/- 0.1. A Comptonized function fits equally well with a Epeak of 118 +/- 35 and alpha of -1.3 +/- 0.2.
The event fluence (10-1000 keV) in this time interval is (1.1 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0-1.5 s in the 10-1000 keV band is 1.6 +/- 0.2 ph/s/cm^2.
The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html
For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"
GCN Circular #42217
A. Volnova (IKI), N. Pankov (HSE, IKI), E. Klunko (ISTP), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN:
We performed optical observations of the field of GRB 251003A, detected by Fermi (Fermi team, GCNC 42069) and Swift (Beardmore et al., GCNC 42070), in the R-filter with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy). The observations began on 2025-10-06 13:10 UT, i.e. ~3.5 days since the trigger and consisted of 90 exposures by 80 s each. The optical source reported previously (Aceituno et al., GCN 42072; Méndez et al., GCN 42073; Strausbaugh et al., GCN 42074; Freeberg et al., GCN 42085; Sanchez-Ramirez et al., GCN 42086; Worssam et al., GCN 42094; Schneider et al., GCN 42095; Mo et al., GCN 42106; Konno et al., GCN 42126) is not detected in the stacked frame. The preliminary photometry is based on nearby USNO-B stars (R2 magnitudes) and is the following:
```
Date         UT start  t-T0         Exp.    Filter   OT   Err.     UL
                      (mid, days)   (n*s)                         (3sigma)
2025-10-06   13:10:16  3.50116      90*80     R      n/d  n/d      22.0
```
GCN Circular #42431
S. I. Chastain (TTU) and A. J. van der Horst (GWU) report:
We carried out follow up observations of GRB 251003A, detected by Fermi (Fermi GBM Team, GCN 42069) and Swift (Beardmore et al., GCN 42070) with the Karl G. Jansky Very Large Array.
At 18 days post-burst (2025-10-21 06:04:43.725), we significantly detect the afterglow at 9 GHz at 40 +/- 5 microJy/beam at the location:
```
RA (J2000): 1:14:07.092 ± 0.003 seconds
Dec (J2000): 56:29:27.94 ± 0.05 arcseconds
```
These observations were taken as part of the Fermi GI project SF181025.
We thank the VLA staff for scheduling and executing these observations.

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Jochen Greiner, last update: 25-Oct-2025 [Disclaimer]